Upgrade to Yarn 4, remove support for Node 16 (#27073)

lib/tasks/webpacker.rake

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+# Disable this task as we use pnpm
+
+require 'semantic_range'
+
+Rake::Task['webpacker:check_yarn'].clear
+
+namespace :webpacker do
+  desc 'Verifies if Yarn is installed'
+  task check_yarn: :environment do
+    begin
+      yarn_version = `yarn --version`.strip
+      raise Errno::ENOENT if yarn_version.blank?
+
+      yarn_range = '>=4 <5'
+      is_valid = begin
+        SemanticRange.satisfies?(yarn_version, yarn_range)
+      rescue
+        false
+      end
+
+      unless is_valid
+        warn "Mastodon and Webpacker requires Yarn \"#{yarn_range}\" and you are using #{yarn_version}"
+        warn 'Exiting!'
+        exit!
+      end
+    rescue Errno::ENOENT
+      warn 'Yarn not installed. Please see the Mastodon documentation to install the correct version.'
+      warn 'Exiting!'
+      exit!
+    end
+  end
+end